Reading between the lines, you may be talking about the case where you have a board with an MCU which can be accessed (download code, debug, etc) via the USB port on your computer. In personal computer peripherals, it has largely been supplanted by other interface standards, such as USB.

FTDI USB-RS232-WE-1800-BT_0.0 - Farnell UK

Where it is necessary to permanently set a control signal to a defined state, it must be connected to a voltage source that asserts the logic 1 or logic 0 levels, for example with a pullup resistor. Those voltages date back to the old electromechanical days of Teletype machines which were a miraculous monstrosity of mechanical marvel. A computer with an RS-232 serial port can communicate with the serial port of an embedded system (such as a router) as an alternative to monitoring over Ethernet. The standard specifies a maximum open-circuit voltage of 25volts: signal levels of ±5V, ±10V, ±12V, and ±15V are all commonly seen depending on the voltages available to the line driver circuit. The standard continued to be revised and updated by the Electronic Industries Association and since 1988 by the Telecommunications Industry Association (TIA).

Since the relation between the transmitted bit and TT can be fixed in the DTE design, and since both signals traverse the same cable length, using TT eliminates the issue. It incorporates FTDI's FT232RQ USB to serial UART interface IC which handles all USB signalling and protocols. No one page will tell you everything but 10 or 20 quick skims will show you how useful it was and how utterly terrible, all at the same time. Serial line analyzers are available as standalone units, as software and interface cables for general-purpose logic analyzers and oscilloscopes, and as programs that run on common personal computers and devices.

RS-232 - Wikipedia RS-232 - Wikipedia

The RS PRO Seal of Approval is your assurance of professional quality, a guarantee that every part is rigorously tested, inspected, and audited against demanding standards. This software communicates with a separate MCU (one that is also on the board with your MCU) via a USB-to-serial converter chip (there are a number of manufacturers for those, as well.Some of our partners may process your data as a part of their legitimate business interest without asking for consent.